Structure built by an animal as a permanent home or for bearing and rearing offspring.
The social insects build systems of chambers and tunnels, above or below ground. Fishes' nests vary from shallow depressions in sand to enclosed structures constructed of vegetation. Certain frog species build mud-basin nests or floating masses of hardened froth. Alligators use mud and vegetation and cobras use leaves and forest litter to build a nest for their eggs. The most common type of bird nest is a cup-shaped or domed structure of twigs, leaves, mud, and feathers. Many mammals, especially small ones, build nests in trees, on the ground, or in burrows.
Nest of the American robin.
(From top) Sven-Olof Lindblad
The National Audubon Society Collection/Photo Researchers; Stephen Dalton
The National Audubon Society Collection/Photo Researchers; Jeff Foott/Bruce Coleman Inc.; G.I. Bernard/OxfordScientific Films